Buffer, yes. But the Maidan protests started because Russia made the first power grab. The very openly pro-Russian government of the time had just passed legislation that put Ukraine on a direct path towards becoming what is now Belarus. TBH, if that hadn't happen, we'd just have Ukraine more or less locked by Putin now. So no, we're not talking about a buffer zone, sorry. Not even in the strict military sense - the invasion today came from Belarus as well, and some reports even claim Belarusian troops, not that it matters much. So without that regime change, we'd most likely see Ukraine as part of the Russian Federation in a military capacity as well.

We _had_ a buffer zone until yesterday. NATO was supporting Ukraine without much real intention of having it join, while Russia had Crimea and half of Donbass. This could have gone for decades - see Transnistria, which does exactly the same for Moldova for 30 years.